The present disclosure relates to systems and methods for the removal of iron sulfide scales in subterranean operations and operations involving the production and/or transportation of oil and gas.
Hydrogen sulfide, H2S, is a naturally occurring contaminant of fluids that is encountered in many industries, including the oil and gas industry and the paper industry. The corrosive nature of H2S and its reaction with steel and other metals used in those industries causes the accumulation of particulate iron sulfide scales. Iron sulfide scale may become entrained in hydrocarbons, glycol, salts, and the like to form deposits on the surfaces in subterranean formations and surfaces of conduits (e.g., pipelines, well casings, production tubing), containers, equipment, and other metal surfaces in oil and gas production. Such deposits may present significant problems, among other reasons, because the deposits may hinder accurate determinations of pipeline structural integrity, block the flow of fluids through conduits, pipelines, or pore spaces in a subterranean formation, and/or interfere with the operation of pumps, valves, and other metal equipment. Severe iron sulfide scaling also may choke production, either in the production tubing, perforations or within the producing formation itself.
Such iron sulfide scales may be removed mechanically (e.g., via milling, scrubbing, or jetting), or an acid (e.g., HCl) or other chemical additive may be used to dissolve or disperse the scales. However, there are significant risks associated with certain acid treatments in high temperature, high-pressure gas wells. These may include corrosivity of acid at high temperature and the generation of toxic H2S gas during the treatment. The acids and other chemicals used in the treatments themselves also may present safety and handling risks.
Moreover, many iron sulfide scale deposits are not homogenous, instead comprising two, three, or more different types of iron sulfides. Depending on factors such as the age of the scale, environmental temperature, and pressure, iron sulfides exist in several distinct forms with different crystalline structures, different ratios of sulfur to iron and different properties. The most common iron sulfide crystalline forms are pyrite (FeS2), troilite (FeS), pyrrhotite (Fe7S8), mackinawite (Fe9S8), and marcasite (FeS2). However, the acid or chemical additive chosen for a particular application may dissolve certain types of iron sulfide scales, but may leave other types relatively undisturbed in the treated area.
While embodiments of this disclosure have been depicted, such embodiments do not imply a limitation on the disclosure, and no such limitation should be inferred. The subject matter disclosed is capable of considerable modification, alteration, and equivalents in form and function, as will occur to those skilled in the pertinent art and having the benefit of this disclosure. The depicted and described embodiments of this disclosure are examples only, and not exhaustive of the scope of the disclosure.